Method of and apparatus for continuous casting



Nov. 13, 1956 1. HARTER, JR, ETAL 2,770,021

METHOD OF AND APPARATUS FOR CONTINUOUS CASTING 3 Sheets-Sheet l INVENTORS ISAAC HARM-R, J'A. TEMPLE WRJTCL/Efi" Filed Oct.

ATTORNEY Nov. 13, 1956 I. HARTER, JR., ETAL 2,770,021

METHOD OF AND APPARATUS FOR CONTINUOUS CASTING Filed Oct. 23, 1952 5 Sheets-Sheet 2 FIG.4

o I nnuuummm Aunnumm- I o o l Fl G.5

ATTORNEY 1956 1. HARTER, JR., ETAL 7 ,0

METHOD OF AND APPARATUS FOR CONTINUOUS CASTING 5 Sheets-Sheet 3 INVENTORJ IJ/IAC HARTER, JR. TEMPLE WR/JTCA/FFF Filed Oct. 23, 1952 tll'll illllll llll FIG."7

HHIiIH ATTORNEY United States Patent METHOD OF AND APPARATUS FOR CONTINUOUS (IASTING Isaac Hatter, Jr., and Temple W. Ratclitfe, Beaver, Pa., assignors to The Babcock & Wilcox Company, New York, N. Y., a corporation of New Jersey Application October 23, 1952, Serial No. 316,446

7 Claims. (Cl. 22-572) The present invention relates to the continuous casting of metal products, and more particularly to improvements in the method of and apparatus for the continuous casting of ingots of ferrous and nonferrous metals and high melting temperature alloys of the general character disclosed in U. S. Patent No. 2,590,311 and a copending application Serial No. 103,901, filed July 9, 1949, now matured into Patent No. 2,682,691.

In the continuous casting of high melting temperature metals such as steel, for example, into ingots of indeterminate length many factors affect the production of a substantially uniform high quality product at a commercially economical rate. These factors include effective control of the rate of molten metal delivery to the mold, the cooling rate of the metal within the mold, and the rate of withdrawal of the casting from the mold. Casting quality control also requires delivery of the molten metal to the mold with a minimum of impurities, such as slag and metallic oxide particles carried over from the furnace or eroded from the molten metal handling equipment or formed by oxidation during the transit of the metal from the furnace to the mold. The quality of the product is also dependent upon effective dimensional and thermal control of the embryo ingot during solidification to avoid cracks in the cast product.

The melting of steel involves the addition of slag-forming materials to the pool or bath of molten metal in the melting furnace for purifying and deoxidizing purposes. Other slag-forming material may be unintentionally added to the molten metal due to erosion of the refractory lining of the furnace during operation and of refractory-surfaced vessels used in handling the molten metal. Ferrous metal in a molten condition is readily oxidizable and when in or passed through an oxidizing atmosphere, such as air, will react to form metal oxides which are carried along in the stream of molten metal. In the continuous casting of steel, the presence of slag and metal oxide particles in the casting mold is deleterious to the cast product. Frequently, slag will cause a complete failure of the casting operation and even if a failure is not involved, the presence of slag during the solidification of the metal may lead to serious defects in the cast ingot.

According to Patent 2,590,311 and said application Serial No. 103,901, commercial rates of steel casting can be attained by the use of high heat transfer rates through the walls of an open ended casting mold to a suitable cooling liquid such as water. When an embryo ingot is formed within the casting mold as described in said patent or said application, the casting leaving the mold will have a molten core, and it is highly desirable in most cases to expedite solidification of the casting immediately after leaving the mold. This solidification step normally involves internal reheating of the ingot shell sufficient to weaken it and cause its expansion under the ferrostatic head of the core. Such shell expansion below the mold, if unrestrained, is concentrated along the weaker side portions of the ingot section and would be conducive to the formation of internal cracks in the solidified casting. It

has been found essential to provide some means for main-- taining axial alignment of the casting with respect to the mold, as well as for effectively limiting the expansion of the casting immediately after it has left the mold and during controlled cooling of the casting, until it has developed sufiicient shell strength to avoid expansion.

In accordance with the present invention, a system of delivering substantially clean molten metal to the continuous casting mold is co-ordinated with means for solidifying the casting shell, withdrawing the embryo casting from the mold, and means for supporting and cooling the casting leaving the mold, so as to attain high production rates of commercially acceptable metallic products. This molten metal delivery system includes means for forming and maintaining a floating slag dam on the surface of the body of molten metal in the melting or holding furnace adjacent the pouring lip of that vessel to hold back the slag from the pouring lip; the discharge of the molten metal through a nonoxidizing atmosphere into a tun dish; the use of a tun dish specially constructed to hold back from its discharge edge any slag particles carried over from the pouring vessel; the maintenance of a special slag layer on the metal in the tun dish; and the maintenace of a nonoxidizing gaseous atmosphere in the upper end of the casting mold.

The supply of molten metal to the mold is controlled, and the casting formed and withdrawn as described in said patents. The quality control is continued by having the casting leaving the casting mold supported by a system of guide rolls whereby any tendency for the casting to expand its cross-sectional dimensions, or to bend out of axial alignment with the casting mold, is restrained by the guide rolls. Depending upon the cross-sectional shape of the casting produced, the guide rolls may be positioned on all sides of the casting, or only on the weak sides of the casting. The guide system used in supporting the casting is cooled by liquid sprays which also serve to cool the casting to complete the solidification of the cast product and to further cool the casting until it has developed sufiicient strength to maintain its dimensions. Where the withdrawal of the casting from the mold is performed in a cycle of changing speeds, the liquid sprays utilized in cooling the casting and the guide system are controlled so that the liquid flow rate delivered by the sprays will be reduced during periods of slow casting withdrawal or casting withdrawal stoppage.

The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understandng of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described a preferred embodiment of our invention.

Of the drawings:

Fig. 1 is an elevation, partly in section, showing the continuous casting mold and the after cooling and guide section constructed in accordance with this invention;

Fig. 2 is an elevation, partly in section, of a pouring vessel, tun dish and the upper end of the continuous casting mold shown in Fig. 1;

Fig. 3 is a vertical section taken on the line 3-3 of Fig. 2;

Fig. 4 is a plan view of the tun dish and its supporting and adjusting mechanism;

Fig. 5 is an end elevation of the tun dish support mechanism shown in Fig. 4;

Fig. 6 is an enlarged plan view of a continuous casting mold such as shown in Figs. 1 and 2 with the upper plates removed;

Fig. 7 is an elevation, partly in section, of the continuous casting mold taken on line 7-7 of Fig. 6; and,

Fig. 8 is a section taken on the line 8?8 of Fig. 1.

While various features of our improved process and apparatus are adapted for use in the continuous casting of both low andhigh melting point metals and alloys, the apparatus described herein is particularly useful for the continuous casting of carbon and alloy steels as well as nickel and other high melting point alloys.

in general, as shown in Figs. l-3, the molten metal to be cast is delivered through the V-notch pouring spout it of a tiltable heated holding or melting furnace ii. The furnace may be equipped for heating by fuel firing, electric induction or electric are means, preferably the last named means. Furthermore, the furnace may be provided with induction stirring devices such as disclosed and claimed in the co-pending application of Isaac Harter, in, Serial No. 304,251, filed August 14, 1952.

The molten metal is delivered from the furnace it at a substantially uniform rate controlled by automatic furnace tilting devices such as disclosed and claimed in the co-pending application of S. 0. Evans and I. Harter, Jr. Serial No. 152,404, now matured into Patent No. 2,709,284. The stream of molten metal discharged from the furnace passes into and through a tun dish 12 before delivery to the upper end of a liquid cooled mold 13. The molten metal is partially or wholly solidified in the mold 13 by heat exchange to a suitable cooling fluid, depending upon the metal being cast, and the solid or embryo casting formed withdrawn through the bottom of the mold by one or more sets of motor driven pinch rolls 14. The solidified casting is cut into desired lentghs by cutting torch 17 or the like, positioned below the pinch rolls 14, and the cut lengths are thereafter removed by a suitable handling mechanism (not shown) to points of storage or use.

In the case of steel, the casting leaving the lower end of the mold consists of a shell of solidified metal with a core of molten metal which contains sufiicient heat to ordinarily reheat the shell to a softened condition, and the ferrostatic pressure of the molten core tends to expand the weakened shell of the casting. For this reason, a series of rollers supported in a latterally resilient sectional framework forms a guide support system 16, which limits the exterior dimensions of the casting and holds the casting in axial alignment during its movement downwardly from the mold 13. The guide support portion of the apparatus is subjected to the cooling effect of a plurality of cooling water sprays which are positioned to impinge water thereon and directly upon the shell of the casting.

In the embodiment of the invention shown in the drawings, the withdrawal pinch rolls 14 are operated with a cyclic change of speed so that the casting will be maintained in a stationary position, or withdrawn at a slow rate, during the dwell portion of each cycle and withdrawn at a relatively high rate of speed during the remainder or run portion of the cycle. In this intermittent type of operation, the cooling water sprays are correspondingly regulated, so that a high rate of water flow contacts the casting during the portion of the cycle in which the casting withdrawal rate is high, while the water flow rate will cease, or be at a relatively low flow rate, when the casting is stationary. The position of the Water sprays relative to the external surface of the casting is co-ordinated in accordance with the cross-sectional shape of the casting and the type of cooling necessary with the particular metal being cast.

As shown in Figs. 2 and 3, the metal holding or melting furnace 11 illustrated is heated by electric arcs formed by electrodes 11 extending through the roof 11 of the furnace. The molten metal bath therein is normally covered by a protective layer of molten slag. The discharge spout 10 of the furnace 11 is provided with a water-cooled lintel 23 positioned inwardly and above the spout. The water-cooled lintel absorbs. radiant heat from the layer of slag covering the surface of the molten metal bath within the furnace .11. The .absorption of heat by the cooling water circulated through the lintel tends to freeze slag on the adjacent upper surface of the metal bath and thereby provide a floating dam of slag 11 across the spout 10 which tends to prevent movement of slag from the furnace through the spout 10 into the tun dish 12. It has also been found advantageous to utilize a slag-forming high melting temperature material such as lime, or dead burned dolomite and lime, which is added to the furnace immediately before the discharge of the molten metal therefrom. The lime, or the like, will remain solid under the temperature conditions maintained in the furnace and will form a nucleus for the accumulation of the normal slag with which to develop the darn.

As shown in Figs. 2 and 3, it has been found advantageous to provide upright panels 25 of sheet metal adiaccnt both sides of the discharge spout 10 and the tun dish 12. Above the spout a sheet of asbestos cloth 24 is attached to a spaced row of horizontally extending rods 24 which rest upon the upper edge of the side pan- C13 25, and forms a flexible top above the molten metal stream. Within the space enclosed by the panels and surrounding the stream of molten metal discharged from the furnace, is positioned an inverted U-shaped burner 26 surrounding three sides of the molten metal stream. A fuel gas is supplied through this burner and is burned around the molten metal stream so as to reduce molten metal oxidation in the zone between the furnace discharge spout 16 and the tun dish 12. Some of the products of combustion resulting from burning the fuel gas will pass through the free space above the molten metal stream passing through the spout, and into the furnace 11. These gases pass through the furnace and escape through the holes in the refractory defining the access doors and the customary roof apertures surrounding the furnace heating electrodes. This flow of gas through the furnace and across the surface of the molten metal therein is caused by the stack effect of the furnace construction, and reduces the oxidation of the molten metal bath therein.

The molten metal discharged from the furnace is re ceived in the tun dish 12 shown in Fig. 2. The dish is of rectangular horizontal and vertical cross-section with an open top at the inlet or furnace end. The end of the dish closest to the furnace 11 is provided with a pocket or recess 31 extending the full width of the tun dish and adapted to receive the stream of molten metal delivered thereto. In the construction shown, the molten metal stream falls with a relatively low velocity due to the relatively short vertical distance between the furnace spout 16 and the surface 32 of molten metal maintained in the tun dish. The falling stream of molten metal penetrates the pool and tends to make a complete reversal in How direction beneath the surface of the molten metal within the confines of the recess 31. The outlet end portion of the tun dish has a cover 2% and a discharge weir 33. The molten metal discharging over the weir 33 to the mold is surrounded by protecting panels 27, and an inverted U-shaped burner 28 is spaced along both sides and the top of the steam discharging from the weir. Between the recess and the weir, a plurality of horizontally spaced transverse depending bafilcs 34 and 35 are provided to serve as shimmers in holding back slag which is placed and collects on the surface of the molten metal in the dish. The slag blanket built up within the tun dish is maintained as a reducing type. When casting steel for example, it is desirable to periodically add sufiicient ferro-silicon to the slag to maintain the reducing nature of the slag.

With the furnace and tun dish construction described, the presence of furnace slag in the stream of molten metal delivered to the mold is substantially eliminated. However, some metal oxides may pass into the mold with the molten metal, or be produced within the mold.

Such oxides should be at a minimum in the mold, but minor quantities thereof will not harm the casting since the casting process hereinafter described causes such oxides to be deposited along the periphery of the casting from which they can be easily removed, and do not affect the quality of the product.

As shown in Figs. 4 and 5, the tun dish 12 is removably mounted on an adjustable frame in a carriage 36 whereby the tun dish may be tilted about a horizontal transverse axis AA. The tilting axis AA is formed by a shaft 41') mounted in trunnion bearings 41 which are in turn supported upon the carriage 36. The tilting of the tun dish about the axis AA is accomplished by a reversible motor 53 connected through a gear reducer 54 to the shaft 40. The motor 53 and reducer 54 are mounted upon a plate bracket 57 attached to and movable with one of a pair of pillow blocks 51 slidably mounted on the carriage side beams 45. The tun dish is thus capable of movement in a direction to increase or decrease the spacing of the dish relative to the mold assembly 13 and the pouring vessel 11. This adjustment is accomplished by a gear motor 42 and a chain drive and sprocket mechanism 43 operable to turn a pair of screw threaded drive shafts 44 positioned on corresponding side beams 45 of the carriage. Each shaft is mounted in bearing brackets 46 attached to the beam 45, and engages a nut 47 which is secured to a depending arm 50 attached to a sliding pillow block 51 supporting the trunnion bearings 41. With the construction described, operation of the gear motor 42 causes the pillow blocks 51 and thus the bearings 41 to move toward or away from the mold assembly 13, depending upon the direction of the rotation of the motor.

The carriage 36 is mounted upon wheels 55 resting on rails 56 for movement in a lateral direction, as is accomplished by means of a gear motor 60 and a detachable tie rod 61 shown particularly in Fig. 4. The tie rod is detachably secured at one end to the carriage 36 while the opposite end is hooked to a clevis 62 to a slidingly movable head 63 which is guided in its movement by slideways 64. The head 63 is moved by a screw-nut mechanism of known type capable of converting the rotational movement of the gear motor 60 output shaft 66 into a lineal movement.

With the arrangement of equipment shown and described, the stream of molten metal discharging from the weir 33 of the tun dish can be adjusted in any direction relative to the fixed position of the mold 13. Such adjustment is extremely important in the delivery of molten metal to a continuous casting mold since it is desirable to have the molten metal stream entering the pool of metal within the mold with a minimum of splatter, without impingement upon the walls of the mold or excessive agitation within the molten core of the embryo casting.

In the plan view of the assembly of furnace, tun dish and mold shown in Fig. 4, the major axis of the horizontally elongated mold shape is in alignment with the centerline of the stream of metal discharged from the weir 33 of the tun dish. The molten metal stream impinges on the pool of metal within the mold adjacent the center of the surface thereof and, due to the trajectory of the delivery stream, has a tendency to wash against the solidified metal forming along the end of the molding tube furthest removed from the tun dish. When other mold shapes are used, such as the nominal square shape hereinafter described and shown in Fig. 8, it is advantageous to deliver molten metal to the mold in a direction normal to the center of a weak side of the casting.

Washing of the solidified metal forming adjacent to the wall of the mold by impingement of the entering molten metal stream has a tendency to weaken and sometimes rupture the weak skin of the embryo casting. When the direction of the falling molten metal stream is such as to impinge on the solidified shell of the casting and when the shell has shrunk, losing contact with the mold wall, any rupture of the casting will cause molten metal to flow therethrough. The molten metal flowing through the ruptured skin will freeze on contact with the mold wall and be attached to the embryo casting to heal the rupture.

When casting elongated cross-sectional shapes it is desirable to form the mold with weak, flat, or outwardly curving ends. With such construction, the ends of the embryo casting will tend to remain in heat exchange contact with the cooling surfaces of the mold, in spite of the shrinkage of the sides of the casting. With such an elongated shape, it is desirable to deliver the molten metal to the mold in a direction normal to the major axis of the casting, and in some cases actually impinging the entering molten metal stream upon the previously frozen metal immediately beneath the molten metal level within the mold to either weaken or cut the casting wall. In casting some metals, such as aluminum, where the entering metal stream is easily directed, it is advantageous to cause the entering stream to weaken or cut the casting on opposite sides of the mold.

The mold assembly 13 shown in Figs. 1 and 2 is disclosed in detail on a larger scale in Figs. 6 and 7. As shown, the mold has a cavity of an elongated horizontal cross-sectional shape with the major axis dimension of the shape positioned parallel to the direction of the molten metal stream discharged from the tun dish 12 (see Fig. 4). As shown particularly in Fig. 7, the mold assembly includes a mold liner 70, pendantly supported by a flange 71, with the lower side of the flange resting upon a horizontally disposed plate 72 which defines the upper wall of a fluid receiving chamber 73. The receiving chamber is provided with a cylindrical member 74 spaced around the mold liner and defining the exterior wall of the chamber. A series of circumferential-1y spaced inlet fittings 75 are fixed in the Wall of the member 74 to receive cooling fluid from the pipes 76 and to provide a distributed flow to the chamber 73. The member 74 is provided with a series of upper and lower lugs 77 and 89, respectively, and fits into a gasketed groove 81 machined in the lower surface of the upper plate 72 and into a correspondingly positioned gasketed groove 82 machined in the upper surface of a lower annular plate 83. The plate 83 is horizontally disposed and machined for bolting attachment to an upright annular weir 84 which is substantially uniformly radially spaced from the exterior surface of the mold liner 70. The upper end of the weir is downwardly spaced from the plate 72 and is further provided with a rounded inner surface which co-operates with the mold liner to provide a converging entrance 85 opening to a cooling fluid or water flow passageway 86 formed between the weir and the mold liner. A supporting skirt member 87 provided with circumferential flanges 90 and constructed in longitudinal sections is detachably secured to the lower portion of the weir 84. In the construction shown, the exterior surface of the mold liner 70 co-operates with the weir 84 and the skirt members 87 to provide a' flow passageway 86 circumferential of the mold liner and having a substantially uniform width throughout its length. A cylindrical baffle 73' acts as a distribution member within the chamber 73.

The top of the mold assembly is provided with a protecting plate 91 of substantially the same dimensions as the plate 72 and having a central opening therein corresponding with the cross-sectional shape of the mold liner 70. A second plate 98 overlying plate 91 is provided with an opening 98 in one side thereof so as to partially cover the open upper end of the mold liner 70 and to provide an opening therein for the stream of molten metal discharged through the weir 33 of the tun dish. The plan view of the second plate is shown in Fig. 4 in its relationship with the mold assembly.

During the continuous casting of high melting temperature metals, such as steel for example, the atmosphere in the upper portion of the mold is controlled to reduce or avoid oxidation of the molten metal. As disclosed in U. S. Patent 2,590,311, this is accomplished by the admission of castor oil, or the like, to the mold in relatively small amounts, and a gas which is not reactive with respect to the molten metal. As shown in Figs. 6 and 7, castor oil is delivered to the mold through a plurality of feed pipes 83 extending to the face of the mold liner 70 through open sided grooves formed in the plate 71. In the embodiment of the invention shown in the drawings, a hydrocarbon gas, such as CzHz, is also introduced into the mold cavity through a pipe 89 extending downwardly through the cover plate 93 into the met cavity above the molten metal level. The hydrocarbon gas is introduced into the mold in small quantities, for example, of the order of 12 liters per hour at atmospheric pressure. The gas is partly burned at a cracking temperature within the mold cavity with the hydrogen released thereby combining with any oxygen present to form water vapor which escapes from the mold during the rise and fall of the molten metal level. When the molten metal level is maintained below a position 6 to inches below the top of the mold liner 7%, it is desirable to introduce a small amount of oxygen to the mold cavity to promote cracking of the gas. Oxygen is only added when the temperature within the mold is insuflicient to crack the gas and some combustion is needed to raise the temperature. This can occur when the molten metal level within the mold is low and the cooling efiect of the upper portion of the mold walls cools the cavity below the gas cracking temperature.

When the continuous casting apparatus is operated with an intermittent withdrawal, as hereinafter described, and the molten metal level rises and falls in a cyclic pattern, the movement of the metal level causes a pumping action on the gaseous atmosphere within the upper portion of the mold cavity. The elfect of this action is to force gases from the mold during the rise of the molten metal level, and to draw exterior gases into the mold cavity during the fall in the molten metal level. The addition of air or other oxygen-containing gases to the atmosphere within the mold cavity should be avoided as much as possible. For this reason, a horizontally arranged U shaped burner 99 is installed upwardly adjacent the plate 8, and positioned to enclose three sides of the molten metal stream entering the mold assembly (Fig. 7). A fuel, such as natural gas, for example, is supplied to the burner, and burned to protect the falling metal stream from oxidation and to insure a substantial absence of oxygen in the gaseous material drawn into the mold cavity as a result of the pumping action of the fall in the molten metal level.

With the arrangement described, the presence of slag and metallic oxides in the molten metal pool maintained in the mold is largely avoided. However, any oxides present in the metal will tend to form a film on the upper surface of the molten metal pool and, with the intermittent casting withdrawal pattern hereinbefore described, the oxide film ruptures and is forced outwardly against the mold wall where it is frozen as a thin skin on the periphery of the casting. The slag or oxide skin on the casting is easily removed, even if the skin does not fall off during the handling and cooling of the casting produced in the apparatus. It has been found desirable to have sufficient rise and fall in the molten metal level during the intermittent operation of the casting withdrawal mechanism to insure that the wall surface covered by the broken film of metal oxide will be covered by the rising molten metal. Generally speaking, the change in level should be sufficient that the area of the mold wall exposed by the fall in the molten metal will be more than twice the area of the mold cross-section,

8 although this relationship will vary with the cross-sectional shape of the mold liner.

The casting 15 discharging from the lower end of the mold liner 70, as controlled in its down movement by the pinch rolls 14, is passed through an after-cooling section where the casting is subjected to the cooling effect of multiple sprays and is supported by a guide system. As shown in Figs. '1 and 8, the guide system consists of a plurality of rollers 92 mounted for rotation in a channel shaped support frame 16 fabricated from a pair of angle irons 93 mounted on a backing member 94. The rollers are shaped to conform to and engage the sides of the descending casting 15 and the frame supporting the rollers is mounted for restraining lateral movement outwardly from the axis of the casting while also being limited as to inward motion. The guide system is arranged in three separate vertically spaced sections for ready lateral adjustment longitudinally of the casting. It will be appreciated that the number of separate guide sections may be greater or lesser than that shown depending upon the support necessary to maintain the dimensions and axial aligment of the embryo casting 15.

In the embodiment shown, the cross-section of the embryo casting 15 is a nominal square with rounded corners and outwardly bowed sides. The rise of the bowed sides is such that shrinkage of the casting will cause the sides to be substantially flat for most of the width when the casting is cold. When casting this shape, it is desirable to provide guide support means on the four sides of the casting. When casting an ingot having an elongated section such as shown for example, in Fig. 6, the guide supports are ordinarily only applied to the long dimension of the elongated shape. The reason for this is primarily due to the need for supporting the weak sides of the casting. All weak sides of a casting should be supported to prevent swelling below the mold.

It will be appreciated that in casting steel or the like, the embryo casting leaving the mold will have a molten interior and there will be a tendency for the casting to expand due to the ferro-static head and shell reheating eliect of the molten metal core, rm'th the pressure of the molten metal tending to distort the shape outwardly of its desired dimensions. In casting with any mold shape, whether it emerges from the mold as an embryo or solid casting, it must also be prevented from swelling or distorting due to columnar loading on the hot relatively weak casting. In the square cross-section shape shown in Fig. 8, all four of the sides of the casting are structurally weak and if unsupported, there would be a tendency for the casting to expand outwardly in the zone below the mold liner 70.

The sectionalized construction of the guide assembly is desirable in permitting a change in the limited lateral position of the guides, as necessitated by the reduction in the cross-sectional dimension of the casting by reason of shrinkage as the casting solidifies. For example, the upper end portion of the guides may be spaced outwardly of the casting centerline more than the spacing at the lower end of the guides. It is also preferable to have a multiplicity of guide sections in order to more closely conform to the cross-sectional size of the casting during cooling.

The after-cooling zone of the continuous casting apparatus is provided with a cincumferentially-spaced series of upright .conduits 95 which receive their water from standpipes 96. The conduits 95 are supported from the frame of the roller guides and extend vertically throughout the vertical dimension of each guide section. The conduits are provided with axially-spaced ports or jets 97 along their entire length for the discharge of cooling liquid under the fluid pressure conditions existing therein. With the casting cross-section shown in Fig. 8, the jets are directed between the rollers and also directly on the rounded corners of the casting. The water collecting on the rollers 92 again contacts the casting to further cool both casting and rollers. The spray contact of the fluid on the hot 9 casting produces some steam which is drawn from the after-cooling section through the exhaust pipe so as to avoid the insulating elfect of the steam. Any hydrogen developed by disassociation of the steam in contact with the hot metal is also withdrawn through exhaust pipe 20.

This regulation of water flow rate is accomplished by means of solenoid valves 19 positioned in the discharge piping of a water circulating pump 22. Ordinarily, the flow rate of the water impacting the casting immediately below the mold will be greater than the flow rate directed against the casting in the lower portion of the aftercooling zone. The amount of cooling water used in the after-cooling zone will vary with the cross-sectional shape and dimensions of the casting, as well as the type of metal being cast. When casting mild carbon steel (i. e. .15 to .20 carbon) in a mold of the shape shown in Fig. 8 and having a cross-sectional area of the order of 50 square inches and at a rate of approximately 750# per minute, for example, the external surface of the casting should not be cooled below approximately 1700 F in the aftercooling zone. In the unit described, the water flow rate through the mold is in excess of 600 gallons per minute, and the average flow rate through the after-cooling section is approximately 100 gallons per minute.

As hereinbefore described, the casting is withdrawn from the mold in an intermittent pattern of lineal withdrawal as for example, 10 second run and 8 second dwell. In such a system of withdrawal, and especially in the case where the casting is withdrawn a definite distance, and then is stationary for a period of time, it is considered highly desirable to stagger the spacing of the ports 97 in the conduits 95 so that the casting 15 at succeeding positions is not exposed to repeated cooling effects during the stationary periods of the casting withdrawal pattern. It will be obvious to those skilled in the art that the casting should not be subjected to bands of spray cooling by an excess of spray water contact, while immediately adjacent sections of the casting may be at a much higher temperature.

The guide support system including the rollers 92 is directly supported upon the standpipes 96 by tubular members 100. Other tubular sleeves 108 are welded into the standpipes and being hollow, are fitted with the tubular members 100 closely fitted therein for sliding movement longitudinally of the sleeves. One end of the sliding tube is welded to the framework supporting the rollers 92 while the opposite end is provided with a compression spring 101 which bears upon a plate 102. The plate 102 is supported by a framework which is welded to the standpipe 96 and is provided with an adjusting screw 103 which is threaded therethrough to bear upon the spring 101.

The tubular members 100 extending horizontally through the standpipes are welded to a cross-beam 104 positioned on each side of the casting 15. The crossbeam 104 is thus free to move in a lateral direction relative to the standpipes 96 on each side of the casting and also provides a support for the framework of the guide rollers 92 on the side of the casting 90 removed from the support rollers 92 guided by the members 100 mounted directly from the standpipes 96. However, cross-beams 104 are adjustably restrained from inward mot-ion beyond a set position by pins 109 and washers 109 on the members 100. As shown in Fig. 8, the spacing between the cross-beams 104 is such as to permit the insertion of a framework supporting the 90-spaced roller guide members. Each of the rollers is mounted in a channel frame 105 which is welded to a bar 106 slidingly engaging a ledge 107 at each end thereof where each ledge is welded to a cross-member 104. The bar 106 is resiliently urged towards the casting by a coil spring 110 which is adjusted by a screw bolt 111 mounted in an outer bar member 112 which slidingly engages the ledge 107 of the transverse members 104. In the embodiment shown, the movement of the bar 106 towards the casting 15 is adjustably I0 restrained by threaded bolts 113 which extend between the outer surfaces of the bars 106 and 112.

As shown in Fig. 8, one end of a rod 122 is welded to one cross beam 104, and a second rod 123 is similarly welded to the companion cross-beam. The rods 122 and 123 are extended in a horizontal direction generally normal to the longitudinal axes of the beams 104. The rod 122 is provided with a scale 124 while the rod 123 is provided with a pointer 125 so that any change in the relative spacing between the cross-beams 104 can be readily observed.

With the casting withdrawal operated in an intermittent pattern of changing speeds, it is desirable to regulate the flow of cooling fluid sprayed upon the casting to correspond with the rate of the casting movement. This is accomplished by enclosing the entire after-cooling section of the apparatus in a housing 114, with the cooling fluid accumulated in a pool positioned at the bottom of the housing. Ordinarily, water is used as a cooling fluid, and a portion of this water is withdrawn from the bottom of the housing by the high pressure pump 22. The discharge duct from the pump is provided with a pair of branch conduits 117 converging into a single discharge pipe 120. The branch conduits 117 are each provided With a screentype filter 119. The discharge pipe is connected to standpipes 96 and the water flow to the spray conduits 95 is controlled by individual manual flow regulating valves 118. The variable flow valves 19 can be of the solenoid type with each operated in concert with the withdrawal mechanism of the pinch rolls 14 so that when the operation of the pinch rolls is stopped, or operated at a low rate, the solenoid valves 19 will be closed or partly closed. For example, the water flow rate may be reduced to 50% or less, of the cooling rate of the run, during the dwell period. When the pinch rolls are again operated at a high Withdrawal rate, the solenoid valves are reopened in concert with the withdrawal speed change. With this type of operation, the amount of cooling water sprayed upon the casting is varied from a high cooling rate during the withdrawal part of the intermittent cycle to a low rate during the dwell or slow speed withdrawal.

The described construction and operation of the continuous casting apparatus is particularly effective for the production of carbon and alloy steel castings free from surface and internal defects, such as cracks and voids. The provisions for minimizing the passage of slag from the furnace to the tun dish and from the tun dish to the mold, the nonoxidizing atmospheres surrounding the molten metal as discharged from the furnace and while in the tun dish and mold, and the casting dimensional control in the after-cooling section, all contribute to the production of a product of high metallurgical quality.

As used in the claims, the term casting is generic in its meaning and includes the concept of a casting having a molten core, or a fully solidified casting section of any temperature distribution.

While in accordance with the provisions of the statutes we have illustrated and described herein the best form of the invention now known to us, those skilled in the art will understand that changes may be made in the process and the form of the apparatus disclosed without departing from the spirit of the invention covered by our claims, and that certain features of our invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. Continuous casting apparatus including an upright liquid-cooled open ended mold, means for delivering molten metal to the upper end of said mold, pinch rolls for withdrawing a casting from the lower end of said mold, and guide means positioned adjacent the lower end of said mold and between said mold and pinch roll for the casting withdrawn from said mold comprising, at least two frames, a plurality of rollers journaled in each of said frames and having their axes lying in a common plane in each frame, structural support members horizontally spaced from the sides of said withdrawn casting, and adjustable means connecting said structural members with each of said frames positioning said frames on opposite sides of said withdrawn casting with the rollers therein in predetermined guiding relationship with said casting.

2. Continuous casting apparatus including an upright liquid-cooled open ended mold, means for delivering molten metal to the upper end of said mold, pinch rolls for withdrawing a casting from the lower end of said mold, and guide means positioned adjacent the lower end of said mold and between said mold and pinch rolls for the casting withdrawn from said mold comprising, at least two frames, a plurality of rollers journaled in each of said frames and having their axes lying in a common plane in each frame, structural support members horizontally spaced from the sides of said withdrawn casting, and adjustable means connecting said structural members with each of said frames for positioning said frames on opposite sides of said withdrawn casting with the rollers therein in predetermined guiding relationship with aid casting, said adjustable means connecting said frames and said structural members each including resilient means for restrained movement of said frame laterally away from the axis of said casting and means limiting the lateral movement of said frame toward the axis of said casting.

3. Continuous casting apparatus including an upright liquid-cooled open ended mold, means for delivering molten metal to the upper end of said mold, pinch rolls for withdrawing a casting from the lower end of said mold, and guide means positioned adjacent the lower end of said mold and between said mold and pinch rolls for guiding and restraining lateral expansion of the casting withdrawn from said mold comprising, a plurality of frames, a plurality of rollers journaled in each of said frames and having their axes lying in a common plane in each frame, structural support members horizontally spaced from the sides of said withdrawn casting, and adjustable means connecting said structural members with each of said frames for positioning said frames in pairs on opposite sides of said casting, said frames disposed in vertically spaced pairs, whereby the axial alignment of the mold and the withdrawn casting is maintained.

4. Continuous casting apparatus including an upright liquid-cooled open ended mold, means for delivering molten metal to the upper end of said mold, pinch rolls withdrawing a casting from the lower end of said mold, and guide means positioned adjacent the lower end of said mold and between said mold and pinch rolls for the casting withdrawn from said mold comprising, at least one pair of frames, a plurality of rollers journaled in each or said frames and having their axes lying in a common plane in each frame, structural support members horizontally spaced from the sides of said withdrawn casting, adjustable means connecting said structural members with each of said frames for positioning said frames on opposite sides of said withdrawn casting with the rollers therein in predetermined guiding relationship with said casting, means for cooling said casting and said rollers by direct spray contact with cooling liquid including valve means for regulating the flow of sprayed cooled liquid whereby the casting is cooled to a surface temperature of not less than l7G0 F.

5. Continuous casting apparatus including an upright liquidcoolcd open ended mold, means for delivering molten metal to the upper end of said mold, pinch rolls for withdrawing a casting from the lower end of said mold, control means for regulating said pinch rolls to Withdraw said casting in a cyclic pattern of changed lineal rates, and guide means positioned adjacent the lower end of said mold and between said mold and pinch roll for the casting withdrawn from said mold comprising, a plurality of frames, a plurality of rollers journaled in each of said frames with their axes lying in a common plane, structural support members horizontally spaced from the sides of said withdrawn casting, adjustable means connecting said structural members with each of said frames positioning said frames on opposite sides of said withdrawn casting with the rollers therein in predetermined guiding relationship with said casting, spray nozzles for projecting cooling Water against said casting and rollers, and valve means for regulating the flow of cooling water to said nozzles in direct relationship to the lineal rate of casting withdrawal.

6. in the continuous casting of metallic products, the

steps which comprise continuously delivering molten metal to the upper end of a fluid cooled mold, forming a casting within said mold, withdrawing said casting in a cyclic pattern of changing lineal speed to vary tie molten metal within said mold between predetermined upper and lower molten metal levels, regulating the cyclic withdrawal of said casting so that the mold wall surface area exposed between said upper and lower molten metal levels is at least double the cross-sectional area of the mold cavity, maintaining the coaxial relationship between said mold and casting while the casting is being withdrawn from said mold cooling the casting immediately below said mold by direct contact with a cooling liquid spray, and varying the rate of spray liquid discharge against said casting with said withdrawal pattern to reduce the rate of liquid discharge during the eriods of reduced lineal withdrawal of said casting from said mold.

7. In the continuous casting of metallic products, the steps which comprise continuously delivering molten metal to the upper end of a fluid cooled mold, forming a casting within said mold by heat exchange with said cooling fiuid, withdrawing said casting in a cyclically changing lineal speed pattern, cooling the casting immediately below said mold by direct contact with a cooling liquid spray, maintaining the cross-sectional dimensions of said casting below said mold and varying the rate of spray liquid discharge against said casting with said cyclic withdrawal pattern to reduce the rate of liquid discharge during the periods of reduced lineal withdrawal of said casting from said mold.

References Cited in the file of this patent UNITED STATES PATENTS 1,324,458 Mclntosh a a. Dec. 9, 1919 1,415,183 Lund May 9, 1922 1,590,730 Evans June 29, 1926 1,814,584 Bost et al, a July 14, 193i 2,050,873 Zickrick Aug. 11, 1936 2,140,607 Thompson Dec. 20, 1938 2,284,503 Williams May 26, 1942 2,376,5l8 Spence May 22, 1945 2,554,836 McFeaters May 29, 1951 2,568,525 Waddington et al Sept. 18, 1951 2,623,531 Waddington et al Dec. 30, 1952 2,698,467 Tarquinee et al. Jan. 4-, 1955 FOREIGN PATENTS 598,385 Great Britain Feb. 17, 1948 633,946 Great Britain Dec. 30, 194.9 656,386 Great Britain Aug. 22, 1951 France Mar. 24, 1947 

